The present invention relates to a process for bringing into contact, with subsequent agitation, of a pulverulent catalytic mass or a mass of a pulverulent adsorbent (pulverulent means that the mass of the solid is in the form of particles such as a powder, extruded grains, beads, dragees, pellets, etc . . . ), the process consisting of agitating the solid in a particular manner.
This process is particularly applicable to stripping particles which are to be separated from a reaction effluent or to regeneration or activation or reactivation or rejuvenation of a catalyst or an adsorbent.
In general for this type of treatment, the catalyst or adsorbent is agitated or swirled in a furnace, in particular in a rotary furnace and for example a louvre type furnace as described in U. S. Pat. No. 4,551,437, in the presence of the reactants necessary for regeneration, activation, reactivation, or rejuvenation, i.e., air or a gas containing oxygen which may or may not be diluted by an inert gas such as nitrogen or any gas capable, for example, of burning the sulphur-containing and carbon-containing contaminants, and under the appropriate operating conditions regarding temperature, pressure, flow rates etc., to carry out this type of impurity burning.
It has been shown that to carry out this type of regeneration or similar treatment or to carry out stripping, it is advantageous to operate such that the catalyst or adsorbent is in the form of a fluid or fluidised bed, as this technology effects excellent heat and matter transfer.
Fluidised bed technology to carry out hydrocarbon conversion reactions is well known, only one example being fluid catalytic cracking. Thus a variety of patents describe that type of arrangement: WO 94-20213, WO 97-39300 and U.S. Pat. No. 4,925,632.
The invention provides a process for bringing a first pulverulent solvent selected from the group formed by catalysts and adsorbents into contact, in a vessel, with a second pulverulent solid with a different granulometry, generally lower than that of the first solid, in the presence of at least one gas.
This process, which causes said solids to move, is particularly applicable to stripping catalysts or adsorbents, or to regeneration of catalysts and adsorbents, or to activation or reactivation or rejuvenation of catalysts or adsorbents.
In this process for bringing particles of a catalyst or an adsorbent into contact with particles of another pulverulent solid, said contact is carried out in a vessel, in the form of a fluid bed by means of a fluidisation gas, the particles of said other pulverulent solid having a granulometry which is different from that of the catalyst or adsorbent particles.
The invention thus essentially concerns bringing pulverulent particles of at least one first solid selected from the group formed by catalysts and adsorbents into contact, with movement, preferably in a fluid or fluidised bed, with inert particles of at least one second solid, the particle size (granulometry) of which is sufficiently different from that of the catalyst or adsorbent to be able subsequently to separate the two solids easily, in particular by screening, in the presence of a gas which is capable of fluidising the two solids, for example air, an inert gas or any gas containing molecular oxygen.
This process can be carried out to effect stripping of a catalyst or any other solid with a view to separating this catalyst or this solid from the gaseous or reacting reactants with which they previously had been brought into contact. Stripping seeks to remove hydrocarbons still present on the catalyst, in particular using any suitable gas, for example air (preferably hot air) or under the action of an inert gas, such as nitrogen, or under the action of steam or carbon dioxide. This process can also be carried out to effect regeneration, reactivation, activation or rejuvenation of a catalyst or an adsorbent.
The second solid can, for example, be alumina, silica, magnesia, sand, mixtures thereof, and dust or fines of these catalysts. In general, the maximum dimension of the particles of the second solid is half that of the smallest dimension of the first solid.
The vessel in which the two solids and the gas such as air are brought into contact is any suitable vessel in which the solids and gases can be agitated. Advantageously, it is a furnace provided at its bottom with a gas distribution system which can fluidise a bed of solid particles.
In a preferred aspect of the invention, the process consists of gradually, periodically or continuously introducing said first solid (catalyst or adsorbent) and said second inert solid at one point (for example one end) of a furnace, together or separately, which gradually advance, i.e., continuously or intermittently (periodically) towards the other end of the furnace. The two types of solids are thus introduced into the vessel, continuously or batchwise, and they gradually, continuously or in batches, advance inside the vessel up to a further point in the furnace (for example to its other end) where they are gradually removed. At least one gas is introduced to at least one point in the furnace, preferably a plurality of points of this furnace, to fluidise the solids. The gas which passes through the catalytic bed has two functions: firstly, fluidisation of the bed to thus ensure good heat and matter transfer in the bed, and secondly as a reactant to participate in the desired reactions in the application under consideration.
When the application is to stripping of a solid containing hydrocarbons, for example, the gas is advantageously air at a moderate temperature or an inert gas such as nitrogen or steam, or finally a mixture of these gases. When the application is to regeneration of a solid containing carbon-containing and sulphur-containing deposits, the gas must be an oxidising gas to permit combustion reactions and in particular it must contain oxygen. The reaction kinetics of carbon and sulphur elimination are controlled by the composition of the gaseous mixture, for example a mixture constituted by greater or lesser quantities of air, nitrogen (to slow down the reaction), and oxygen (to accelerate the reaction). When the application is too activation, reactivation, or rejuvenation, specific reactive gases can be used, either alone or as a mixture, for example hydrogen, hydrogen sulphide, ammonia, chlorine-containing compounds . . . At the vessel outlet, where the first solid (catalysts or adsorbent) and the inert solid are removed, the two solids can be separated by screening, the catalyst or the stripped solid or the catalyst, or the regenerated or reactivated or activated or rejuvenated adsorbent being recovered, also the inert solid. Advantageously, at least a portion of the inert solid is recycled to the catalyst or adsorbent treatment vessel. This in particular retains a suitable heat level.
In accordance with the present invention, it will be noted that the catalyst or adsorbent can be treated in one vessel or in a number of vessels in series, if a single vessel is not sufficient. It is also possible to pass the catalyst or adsorbent through the same vessel several times.
Inside the vessel in which the solid to be treated (catalyst or adsorbent) is brought into contact with the fluidisation gas, and in particular in the case when this vessel is a rotary furnace, where solids are introduced at one end of the furnace, internal means such as baffles are advantageously disposed in the furnace or vessel to force the catalyst or adsorbent to circulate from the entry point into the vessel to the outlet point. These internal means can, for example, be a simple metal plate, or (at least) two plates disposed across the vessel, for example, which thus divide the vessel or furnace (for example cylindrical) into 2 or (at least) four zones, The temperature in the vessel is regulated in different manners: firstly, the quantity of external energy supplied to the system by the electrical resistances, gas burners, exchangers or any other suitable means; secondly the quantity of energy extracted from the system by cooling systems such as tube or plate exchangers traversed by a cooling fluid such as air, steam, water or oil; finally, the gas composition, the flow rate of the solid to be treated and the flow rate of the inert solid recycle. To regenerate the catalyst, for example, it is possible to operate at 500xc2x0 C. with solids which pass through the vessel in about 1 or 2 hours. If regeneration is involved, the gas containing molecular oxygen is introduced in a quantity sufficient to obtain stoichiometric burning of the carbon-containing and sulphur-containing deposits, or at least a 50% burning rate.
The essential feature of the present invention is to have a sufficient gas flow rate to ensure fluidisation of the first solid and a sufficient gas flow rate to ensure at least 50% combustion of the carbon-containing and sulphur-containing deposits.
An alumina can be used as the inert solid, such as an electrofused alumina (for example with a density of 1700 kg/m3 and with a granulometry of less than 500 microns, preferably 20 to 300 microns, more particularly with an average granulometry of 150 microns). As indicated above, it can also be sand or other solids with granulometries of the same order of magnitude as for the alumina. It is also possible to use a product analogous to the catalyst used in catalytic cracking oil refining units with a granulometry of about 50-80 microns, for example. It is also possible to use fines or dust obtained during manipulation or treatment of various products and in particular products of the same nature as those which are to be treated, namely catalysts or adsorbents. The granulometrical distribution will be adjusted by known techniques for separating pulverulent solids, such as cycloning or screening.
The fluidisation gas flow rates required in the present invention are much lower than those normally used for fluidisation in the absence of a second, inert, solid. By way of example: a linear velocity of 1 m/s (metres per second) is required to fluidise extrudates with a diameter of 1.6 mm with an apparent density of 830 kg/m3; a rate of 1.5 to 1.8 m/s is required to fluidise beads with a diameter of 2.4 with an apparent density of 680 kg/m3; a rate of 2.2 m/s is required to fluidise alumina beads with a diameter of 0.1 to 0.2 with an apparent density of 1200 kg/m3. However, if the catalyst is diluted by an equivalent quantity of alumina (inert solid) with an average granulometry of 100-200 microns, fluidisation can be achieved with a linear velocity of 0.2 m/s of air.
Using the process of the invention, the particles of catalyst or adsorbent remain properly dispersed without the particles floating or descending or plunging to the bottom of the vessel. The catalyst or adsorbent particle size is in general in the range 0.5 to 5 millimetres and more frequently in the range 0.8 to 3 mm. The ratio of the catalyst or adsorbent with respect to the inert solid is in the range 0.1 to 1 by weight, preferably in the range 0.1 to 0.3.
As indicated above, the gas can be air diluted to a greater or lesser extent, with the oxygen content being varied by adding pure oxygen or by adding nitrogen or another inert gas, or by dilution with at least a portion of the combustion gases.
As indicated above, the furnace can be constituted by a plurality of zones, for example rectangular in nature with forced circulation from zone to zone through a series of baffles located between the inlets and outlets for the various zones. It is possible to use not a single furnace but a series of furnaces connected together with independent temperature regulation and gas flow rates which can differ from one zone to another of the zones. These zones can be disposed in series or in parallel.
With rotary louvre furnaces or belt furnaces, the present invention has the advantage of having better temperature control and of obtaining short residence times. The better the heat can be evacuated while controlling the bed temperature, the faster suitable burning is obtained by increasing the oxygen content of the gas mixture. The presence of a large mass of inert solid also enables the temperatures to be controlled by preventing the formation of hot spots.
A further major advantage of the process of the invention is to be able to treat mixtures of different catalysts with different granulometries, which is not possible in a direct fluidisation furnace without using an inert solid.
The process of the invention can also reduce the attrition rates and thus the formation of fines, it can homogenise catalysts better, i.e., fewer erratic movements of catalyst particles are observed.